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<span id="Code-Iterators"></span><div class="header">
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<hr>
<span id="Code-Iterators-1"></span><h4 class="subsection">17.23.2 Code Iterators</h4>
<span id="index-code-iterators-in-_002emd-files"></span>
<span id="index-define_005fcode_005fiterator"></span>
<span id="index-define_005fcode_005fattr"></span>

<p>Code iterators operate in a similar way to mode iterators.  See <a href="Mode-Iterators.html">Mode Iterators</a>.
</p>
<p>The construct:
</p>
<div class="example">
<pre class="example">(define_code_iterator <var>name</var> [(<var>code1</var> &quot;<var>cond1</var>&quot;) &hellip; (<var>coden</var> &quot;<var>condn</var>&quot;)])
</pre></div>

<p>defines a pseudo rtx code <var>name</var> that can be instantiated as
<var>codei</var> if condition <var>condi</var> is true.  Each <var>codei</var>
must have the same rtx format.  See <a href="RTL-Classes.html">RTL Classes</a>.
</p>
<p>As with mode iterators, each pattern that uses <var>name</var> will be
expanded <var>n</var> times, once with all uses of <var>name</var> replaced by
<var>code1</var>, once with all uses replaced by <var>code2</var>, and so on.
See <a href="Defining-Mode-Iterators.html">Defining Mode Iterators</a>.
</p>
<p>It is possible to define attributes for codes as well as for modes.
There are two standard code attributes: <code>code</code>, the name of the
code in lower case, and <code>CODE</code>, the name of the code in upper case.
Other attributes are defined using:
</p>
<div class="example">
<pre class="example">(define_code_attr <var>name</var> [(<var>code1</var> &quot;<var>value1</var>&quot;) &hellip; (<var>coden</var> &quot;<var>valuen</var>&quot;)])
</pre></div>

<p>Instruction patterns can use code attributes as rtx codes, which can be
useful if two sets of codes act in tandem.  For example, the following
<code>define_insn</code> defines two patterns, one calculating a signed absolute
difference and another calculating an unsigned absolute difference:
</p>
<div class="example">
<pre class="example">(define_code_iterator any_max [smax umax])
(define_code_attr paired_min [(smax &quot;smin&quot;) (umax &quot;umin&quot;)])
(define_insn &hellip;
  [(set (match_operand:SI 0 &hellip;)
        (minus:SI (any_max:SI (match_operand:SI 1 &hellip;)
                              (match_operand:SI 2 &hellip;))
                  (&lt;paired_min&gt;:SI (match_dup 1) (match_dup 2))))]
  &hellip;)
</pre></div>

<p>The signed version of the instruction uses <code>smax</code> and <code>smin</code>
while the unsigned version uses <code>umax</code> and <code>umin</code>.  There
are no versions that pair <code>smax</code> with <code>umin</code> or <code>umax</code>
with <code>smin</code>.
</p>
<p>Here&rsquo;s an example of code iterators in action, taken from the MIPS port:
</p>
<div class="example">
<pre class="example">(define_code_iterator any_cond [unordered ordered unlt unge uneq ltgt unle ungt
                                eq ne gt ge lt le gtu geu ltu leu])

(define_expand &quot;b&lt;code&gt;&quot;
  [(set (pc)
        (if_then_else (any_cond:CC (cc0)
                                   (const_int 0))
                      (label_ref (match_operand 0 &quot;&quot;))
                      (pc)))]
  &quot;&quot;
{
  gen_conditional_branch (operands, &lt;CODE&gt;);
  DONE;
})
</pre></div>

<p>This is equivalent to:
</p>
<div class="example">
<pre class="example">(define_expand &quot;bunordered&quot;
  [(set (pc)
        (if_then_else (unordered:CC (cc0)
                                    (const_int 0))
                      (label_ref (match_operand 0 &quot;&quot;))
                      (pc)))]
  &quot;&quot;
{
  gen_conditional_branch (operands, UNORDERED);
  DONE;
})

(define_expand &quot;bordered&quot;
  [(set (pc)
        (if_then_else (ordered:CC (cc0)
                                  (const_int 0))
                      (label_ref (match_operand 0 &quot;&quot;))
                      (pc)))]
  &quot;&quot;
{
  gen_conditional_branch (operands, ORDERED);
  DONE;
})

&hellip;
</pre></div>

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